There's even more possibilities with multi channels. For years I've used a plug-in from Creo that was formerly called Powertone Inks and it allows for a kind of simulated 4-color by using two inks (hasn't been updated in years though). I use a blue-green and a red-orange that when combined print excellent skin tones and generally look great except for the lack of greens in foliage. What also is quite impressive is that a black is produced and images can also look like black and white half tones for those that were originally black and white. The only problem with the DCS format (a big one!!!) is that it only allows 72 dpi previews and that when proofing the images are printed at 72 dpi, while the separations are at the normal resolutions for the file (225 or 300 dpi etc.).